Caselli, Graziella, author
Elsevier, 2005
Buku Teks
Nam, Charles B.
Hoghton Mifflin., 1976
Buku Teks
Thomlinson, Ralph, author
Random House , 1976
Buku Teks
edited by Philip M. Hauser and Otis Dudley Duncan
The University of Chicago Press, 1959
Buku Teks
Woytinsky, W.S.
The Twentieth Century Fund, 1953
Buku Teks